Cost-effective microabsorbance detection based nanoparticle immobilized microfluidic system for potential investigation of diverse chemical contaminants present in drinking water

The measurement of the concentration of different heavy-metal ions present in the water environments is becoming increasingly essential as water-pollution concerns worsen. The optical sensor has become a good platform for detecting heavy-metal-ion concentration due to its compact size; chemical inertness; and anti-electromagnetic interference. Here, we propose to fabricate a simple and cost-effective microfluidic device for the detection of aqueous-heavy-metal ions such as lead(II), chromium(III) and mercury(II) using an optical-micro-absorbance-spectroscopy/LSPR based principle. Firstly, a disposable-PDMS-micro-device with a rectangular "Z-shaped microfluidic channel" integrated with micro-lens-structure and optical-fibre-coupler-structure was fabricated via cost-effective soft-lithography-technique using a microfabricated SU8 master. Further, the synthesized-Silver-Nanoparticles were also immobilized inside the microchannel structure in some of the micro-devices for nanoparticle-based-sensing studies. The real-time presence of heavy metal ions in the minuscule sample volume was analyzed by passing different-sample concentrations intermittently through the abovementioned microfluidic structure and measuring the bulk-micro-absorbance across its enhanced optical path length coupler-structure. The results specify that the fabricated micro-device can be easily utilized for label-free detection of a minimum of 0.5 ppb for all the aforesaid sample-heavy metal ions. The absorbance-change observed per unit concentration-change of Lead ion, mercury ion and chromium ion (from 0.001 to ∼50 μg/ml) is found on average-1.8 × 10-2 ΔA/μg/ml, 1.1 × 10-2 ΔA/μg/ml, 4.2 × 10-3 ΔA/μg/ml, respectively. For silver nanoparticle-based studies, the absorbance-change observed per unit concentration change of aforesaid heavy-metal-ions (i.e. the sensitivity) was found on average ∼2 times higher in comparison to simple micro-absorbance-based studies. Additionally, the micro-device has a capability for simplistic incessant(real-time)investigation, a preset-analyte-quantity-interface, and management over the injected analyte-evaporation.